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LTC3810 参数 Datasheet PDF下载

LTC3810图片预览
型号: LTC3810
PDF下载: 下载PDF文件 查看货源
内容描述: 60V低IQ ,双通道,两相同步降压型 [60V Low IQ, Dual, 2-Phase Synchronous Step-Down]
分类和应用:
文件页数/大小: 40 页 / 464 K
品牌: Linear Systems [ Linear Systems ]
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LTC3890  
operaTion (Refer to the Functional Diagram)  
Main Control Loop  
Shutdown and Start-Up (RUN1, RUN2 and  
TRACK/ SS1, TRACK/SS2 Pins)  
The LTC3890 uses a constant frequency, current mode  
step-down architecture with the two controller channels  
operating 180 degrees out-of-phase. During normal op-  
eration, each external top MOSFET is turned on when the  
clock for that channel sets the RS latch, and is turned off  
when the main current comparator, ICMP, resets the RS  
latch. The peak inductor current at which ICMP trips and  
resets the latch is controlled by the voltage on the ITH pin,  
which is the output of the error amplifier, EA. The error  
amplifier compares the output voltage feedback signal at  
The two channels of the LTC3890 can be independently  
shutdownusingtheRUN1andRUN2pins.Pullingeitherof  
these pins below 1.15V shuts down the main control loop  
for that controller. Pulling both pins below 0.7V disables  
both controllers and most internal circuits, including the  
INTV LDOs. In this state, the LTC3890 draws only 14µA  
CC  
of quiescent current.  
Releasing either RUN pin allows a small internal current to  
pull up the pin to enable that controller. The RUN1 pin has  
a 7µA pull-up current while the RUN2 pin has a smaller  
0.5µA. The 7µA current on RUN1 is designed to be large  
enough so that the RUN1 pin can be safely floated (to  
always enable the controller) without worry of condensa-  
tion or other small board leakage pulling the pin down.  
This is ideal for always-on applications where one or both  
controllersareenabledcontinuouslyandnevershutdown.  
the V pin, (which is generated with an external resistor  
FB  
divider connected across the output voltage, V , to  
OUT  
ground)totheinternal0.800Vreferencevoltage.Whenthe  
load current increases, it causes a slight decrease in V  
FB  
relative to the reference, which causes the EA to increase  
the ITH voltage until the average inductor current matches  
the new load current.  
After the top MOSFET is turned off each cycle, the bottom  
MOSFETisturnedonuntileithertheinductorcurrentstarts  
to reverse, as indicated by the current comparator IR, or  
the beginning of the next clock cycle.  
The RUN pin may be externally pulled up or driven directly  
by logic. When driving the RUN pin with a low impedance  
source, do not exceed the absolute maximum rating of  
8V. The RUN pin has an internal 11V voltage clamp that  
allows the RUN pin to be connected through a resistor to a  
INTV /EXTV Power  
CC  
CC  
highervoltage(forexample,V ),solongasthemaximum  
IN  
current into the RUN pin does not exceed 100µA.  
Power for the top and bottom MOSFET drivers and most  
other internal circuitry is derived from the INTV pin.  
CC  
The start-up of each controller’s output voltage V  
is  
OUT  
When the EXTV pin is tied to a voltage less than 4.7V,  
CC  
controlled by the voltage on the TRACK/SS pin for that  
channel. When the voltage on the TRACK/SS pin is less  
than the 0.8V internal reference, the LTC3890 regulates  
the V LDO (low dropout linear regulator) supplies 5.1V  
IN  
from V to INTV . If EXTV is taken above 4.7V, the V  
IN  
CC  
CC  
IN  
LDO is turned off and an EXTV LDO is turned on. Once  
CC  
the V voltage to the TRACK/SS pin voltage instead of the  
FB  
enabled, the EXTV LDO supplies 5.1V from EXTV to  
CC  
CC  
0.8V reference. This allows the TRACK/SS pin to be used  
toprogramasoft-startbyconnectinganexternalcapacitor  
from the TRACK/SS pin to SGND. An internal 1µA pull-up  
current charges this capacitor creating a voltage ramp on  
the TRACK/SS pin. As the TRACK/SS voltage rises linearly  
from 0V to 0.8V (and beyond up to 5V), the output voltage  
INTV . Using the EXTV pin allows the INTV power  
CC  
CC  
CC  
to be derived from a high efficiency external source such  
as one of the LTC3890 switching regulator outputs.  
Each top MOSFET driver is biased from the floating boot-  
strap capacitor, C , which normally recharges during each  
B
V
OUT  
rises smoothly from zero to its final value.  
cycle through an external diode when the top MOSFET  
turns off. If the input voltage, V , decreases to a voltage  
Alternatively the TRACK/SS pin can be used to cause the  
start-up of V to track that of another supply. Typically,  
IN  
close to V , the loop may enter dropout and attempt  
OUT  
OUT  
to turn on the top MOSFET continuously. The dropout  
detector detects this and forces the top MOSFET off for  
about one twelfth of the clock period every tenth cycle to  
this requires connecting to the TRACK/SS pin an external  
resistor divider from the other supply to ground (see the  
Applications Information section).  
allow C to recharge.  
B
3890fb  
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